1. Field of the Invention
The present invention relates to a sound insulation cover that can be suitably applied to a noise source such as the exhaust manifold of an engine for an automobile.
2. Description of the Background Art
There have been widely employed sound insulation covers each of which is externally mounted on an exhaust manifold so as to insulate noises from the exhaust manifold to improve quietness in a vehicle and so as to insulate heat from the exhaust manifold to prevent thermal degradation of a harness disposed near the exhaust manifold.
For example, patent document 1 proposes the following technology: a steel plate plated with aluminum and having sound-absorbing and heat-insulating material put thereon in layers is used as a sound insulation cover; and a support jig for supporting the sound insulation cover on an exhaust manifold is composed of a cylindrical part into which a fastening bolt is inserted, a grommet that has a flange extending outside in a radial direction formed on one end of the cylindrical part and that has a small-diameter stepped portion formed on the other end of the cylindrical part, a washer fitted in the small-diameter stepped portion, and a pair of ring-shaped elastic bodies that are fixedly mounted in advance on the one end surface of the washer and on the inside surface of the flange and that are formed by knitting stainless wires, the washer being fixed to the grommet by a fastening portion formed by plastically deforming the small-diameter stepped portion outward in the radial direction to support the sound insulation cover in a state where the sound insulation cover is pinched between the pair of elastic bodies.    Patent document 1: Japanese Unexamined Patent Publication No. 2004-245076
By the way, demands for a reduction in weight in passenger cars are increasing to promote energy savings as much as possible, so there have been employed the sound insulation covers constructed of light-metal plates made of aluminum alloy or the like in place of steel plate. However, vibrations caused when the car is running and vibrations from the engine are transmitted to the sound insulation cover via the exhaust manifold. Thus, when the sound insulation cover is constructed of material having low mechanical strength such as aluminum alloy, even if the support jig described in the patent document 1 is used, there is presented a problem that the relative displacement between the exhaust manifold and the sound insulation cover, caused by the vibrations, cannot be sufficiently absorbed to cause cracks owing to secular changes at the portion where the sound insulation cover is fixed to the exhaust manifold.